Paraffin oil was encapsulated in a urea-formaldehyde polymer shell by in situ polymerization. The effect of modifying the fabrication parameters, specifically the emulsifier, the core material concentration, the stirring rate, and the pH, on the resulting microcapsules was characterized by FTIR, SEM, particle size analysis and TGA. The stiffness and the mechanical stability during mixing of the microcapsules were also evaluated. It was found that the ethylene maleic anhydride copolymer (EMA)-based microcapsules are smaller, harder and have an increase in yield of 15 % or more compared to the polyvinyl alcohol (PVA)-based microcapsules. Both EMA- and PVA-based microcapsules have good thermal stability up to 400 A degrees C. Smaller EMA-based microcapsules require a higher force, up to 0.96 N, to be 80 % deformed.